In recent years, global environmental problems due to an air pollution have become obvious, and in the context to tightening of regulations on emission gas from plants and vehicles, a gas detection apparatus has been required to be highly sensitive. In terms of an environmental standard related to the air pollution, for example, 40 ppb (parts per billion) or less has served as a standard for NOX (nitrogen oxide), and thus, detecting an extremely small amount of gas component in the order of ppb has been required. Separately from the environmental problems, in the defense field, development of accurate and rapid analytical methods with respect to NBC (Nuclear Biological Chemical) substances has stood as an issue. In terms of chemical agents in particular, rapid sensing of toxic gas that has an extremely strong effect on human body has been required as seen in the sarin nerve-gas attack on the Tokyo subway system. In order to prevent secondary damage, it is necessary to detect a gas component having an extremely low concentration in real time. Although various methods have been known as a method of detecting a gas component having a relatively high concentration, the detection methods have been limited for detecting the gas component having a concentration of ppb (parts per billion) to ppt (parts per trillion), which corresponds to an extremely low concentration.
For example, at a disaster site or a site at which an act of terrorism occurs or the like, it has been desired to sense the risk in advance by detecting an extremely small amount of the gas component. The gas component having an extremely low concentration is often detected by use of a large equipment in research facilities. In this case, a large sized installation type equipment, which is expensive and has large weight and volume, such as a gas chromatography or a mass spectrometer, is required. The case when direct measurement is desired on the go relies on a simple measurement method that detects the gas component by use of a biological reaction mechanism, but has many problems of a storage life, temperature management, a limit of determination whether the gas component is present or not, and the like. Under such circumstances, it has been required to provide an apparatus that is capable of detecting the gas component having an extremely low concentration in real time, in other words, an apparatus that has a smaller weight and volume and a better portability and enables selective and higher sensitive detection of the gas component having an extremely low concentration in the order of ppt to ppb.
As a detection element for the gas component having a low concentration, for example, an element has been known that has a conductive layer in which a surface of a carbon nanostructure is surface modified with an organic substance or the like that selectively reacts with or adsorbs a specific substance and measures a potential difference or the like that changes depending on the gas component that has adhered to the surface of the carbon nanostructure. When a component or the like similar to detection target gas component is mixed, as an impurity, in gas obtained from the air, such a detection element has a risk of being incapable of accurately detecting the detection target gas component. Further, types of the organic substance that reacts with or adsorbs the detection target gas component (gas molecules) themselves are also limited and only the modification of the surface of the carbon nanostructure or the like with the organic substance is not sufficient, resulting in a difficulty in further increasing detection accuracy of the gas component.